class User{
    fullName:string
    firstName:string
    lastName:string
    constructor(firstName:string,lastName:string){
        this.firstName=firstName
        this.lastName=lastName
        this.fullName=firstName+lastName
    }
}
interface Person{
    firstName:string
    lastName:string
}

function greeter(person:Person){
    return "Hello"+person.firstName+''+person.lastName;
}

let user=new User('Yeea','Huang');
console.log(greeter(user))